Means for electrically reproducing sound



Sept. 26,1933. A. HEWITT 1,928,426

MEANS FOR ELECTRICALLY REPR ODUCING SOUND Filed 1924 2 Sheets-Sheet 1 Sept. 26, 1933. w T-r 1,928,426

MEANS FOR ELECVI'RICALLY REPRODUCING SOUND Filed Dec. 17, 1924 2 Sheets-Sheet 2 l l fii m m i 1 the vibratory elements of a sound box to elimi- These'devices haveebeen unsatisfactory in that r r .larged, illustrating one'manner in which the Patented Sept. 26, 1933 I .jisam' MEANS FOR'ELECTRICALLY V. SOUND nsraonuomd Albertis Hewitt, Pitman, N..J., assignor, by mesne assignments, to Radio Gorporation'of America, 1 "New York,.Np?Y-.,; a corporationof Delaware.

a Application necember 17,1924

Serial'No.'756,571

,g euas. (01. 179-10041) This invention relates to. the reproduction of sound, and more particularly tov amethod and means, for electrically reproducing sound from talking machinerecords. I, 1 1

It has heretofore been proposed to reproduce sound electrically'from talking machine records, and, to amplify the reproduction by suitable means including the use of thermionic valves.

the amplification: has, increased the volume of foreign or irregular sounds, such as are produced by the engagement of ftheneedle orstylus on the record, etc.,' as well as thevolume of the pure or. musical sounds.

. It has also been proposed, heretofore, to dampen nate undesirable noises.) and irregularities of soundsuch as are produced by the mechanical engagement of the soundreproducing elements.

This dampening, however, has invariably resulted in the distortion and suppression of the pure as well as the irregular sounds. 1

An object of the present invention is to provide a novel -method. and means for electrically reproducing sounds from a record'tablet. so as to minimize the harsh and irregular sounds or noises while amplifying the puresounds' to anydesired volume.

Another object of the invention is to provide a method, and, means for electrically "reproducing 'a record tablet by dampening the mechanical vibrations produced by the action of a stylus or needle cooperating with said tablet, converting the dampened mechanical vibrations intoelectrical vibrations, amplifying the latter; and converting the same into sound waves. f j y Another object of the invention is to provide, in combination, a dampened stylus bar, a dampened armature actuated by the bar, and suitable means for amplifying the electrical vibrations' produced; by thev dampened mechanical vibrations of the stylus bar and armature.

I Other'objects of the invention are to provide means of the characterdescribed whichmay be employed in combination with talking machines now in use,which are rugged in construction,

and which are readily'accessibleforrepair. Ihese and other objects will appear more fully herein- The invention will be readily understood by reference to the accompanying drawings illustrat ing one embodiment of the inventive idea, but it is to be expressly ,understood'that the drawings are for purposesof illustration only and are" not designed as a definition; of thelirjnitsof. the in 'armatureof the reproducer, may bedampenedi .Fig; 5 is a'detail perspective illustratinga preferred form-ofstylusjbar; x p Fig.6 is a detail" sectional view taken on'fli'n'e 6+6 of Fig. 1; w

Fig. "7" is a detail view; partly in"section ,f1llustrating a portion of the'stylus bar mounting; I

that may be employed in the reproducenand Fig. 9 is a diagrammatic view illustrating one combination otelements that may be employed for carrying out the method of the'present inven tion. 5' Y Referring to the drawings, whereinjlikerefer ence characters refer to like partsthroughoutthe several views, 10 is a shell or casing of any suitable form' and material that at its forward faceis bent inwardly to form a circular shoulder 11. A cup 12, of any suitable material, suchas aluminum, and providedwith a central opening 12, is main- Fig. 3 is a perspective of one of the polepieces tainedin engagement with. shoulder, 11 in any suitable way, as by means of a cylindrical ber 13. Preferably, the latter is formed of asuitable dielectric' such as vulcanized rubber. The opposite orrear endof the chamber formedby the member 13 is closed by a disk 14, which consti tutes an insulating membenand which isfmaintained in position by'means of a disk-like cover 15 which is removably secured to the rear end of casing 10 in any suitable manner as by means of screws 16. W

Mounted within the chamber formed by 'the elements 12, 13 and l ldescribed above, isfa permanent magnet 17 of any suitable construction, shown as a circular magnet which'is divided at one side to provide spaced poles 17' that are located on the opposite sidesof the medialplane of the magnet. Secured to therinner surface of each pole 17, as by means of screws 18, is a U-shaped pole piece 1901 20 which extends radially inward "fromits pole and which is so mounted that its tioned between the limbs of pole pieces 19;, and

: eliminated or suppressed and ture 24 is preferably such that it extends both above and below the limbs of the pole pieces 19 and 20.

Suitably secured to the front face of the upper end of armature 24, and centrally thereof, is an L-shaped stylus bar 25. The upper horizontal limb 25', of this bar, whichis preferablyin the: form of a wire to provide suitable lateral flexibility, extends outwardly through the opening 12 in cup 12, and. a groove 20 may be formed in the upper surface of the inner limb of the pole piece 20 to receive said horizontal limb 25.

Any suitable means may be provided for op,- eratively mounting the stylus bar on the casing 10. The present invention, however, includes a novel mounting which is productive of superior results. In the form shown .a bar 26 extends horizontally across the forward face of casing 10 andadjacent the lower portion thereof and is preferably formed integrally with said casing.

Secured in any desired manner to the front face' of bar 26 is aknife-edge 27 which extends parallelwith the axis of the bar 26 and at right angles to the axis'of stylus bar 25. symmetrically mounted on the front face of bar 26, in planes parallel to thestylu's bar 25 and equidistant therefrom, area pair of T-shape'd lugs 28 '(see Fig. 7) which receive andretain in cooperative position a pair of U-shaped springs 29 which are suitably secured, as by means of brazing, to the opposite sides of stylus bar 25 in the plane of knife-edge 27.. Lugs. 28, springs 29' and knifeedge 27 are so proportioned that the springsv are maintained in a flexed condition, as is clearly illustrated in Fig. 6, when the stylus bar is engaged with the knife-edge 27 and the springs 29 have their U-shapedends engaged under the lugs 28. The usual stylus or needle 30 and retaining means 31are provided at the lower end of the stylus bar 25.

Suitable damping means arepreferably provided for dampening the natural vibration of stylus bar25 and also for preventing whipping of the same. In the form shown, this dampening means comprises a rubber tube 32 which surrounds the stylus bar and extends from the armature 24 outwardly and downwardly to the upper edge of springs 29.

Means of any suitable type are also provided fordampening the mechanical vibrations imparted to armature 24 by the cooperation of the stylus or needle 30 with a rotating record tablet, in order that the irregular vibrations or noises, such for example. as are caused by the engagement of the needle on the record tablet may be that the periodic vibrations of the pure or musical sounds only will be available for actuating the armature to induce currents of variable E. M. F. in coil 22.

In the form shownKFigs. 2, 3 and 4) this dampening means comprise a pair of elongated blocks 33, preferably formed of compressed rubber, which are interposed between the ends of the limbs of one'of the pole pieces, as 19, and armature '24, said blocks being preferably secured to the former, and co-act'with said armature adjacent the opposite ends thereof. While the drawings illustrate the use of two dampening blocks, one block for each limb of pole piece 19, it is to be expressly understood that one block may be employed on each side of the armature if desired, or other arrangement of the dampening blocks may be used.

Secured to the cup 12 and projecting within the magnet 17 are binding posts 34 to which are attached conductors 35 that are placed in electrical'communication, in any well known manner, with the opposite ends of coil 22. Conductors 35 pass rearwardly through openings in insulating disk 14 and rear cover plate 15 to a suitable amplifying circuit such, for example, as that diagrammatically illustrated in Fig. 9, where- .in the thermionic valves 36 amplify the currents produced in coil 22 and deliver said amplified currents to a loud speaker 37 of any suitable type.

A neck 38 (Fig. 2) of any suitable form may be formed on the rear of plate 15 to constitute means for securing the reproducer unit to a movable arm 39 (Fig. 9). This arm is mounted in any suitable way adjacent a turntable 40 that is adapted tocarry the usual record tablet 41.

, Operation- -Rotation of the turntable 40, and consequently of the tablet 41, results in the vibration of stylus bar 25, and thevibrations of said bar are transmitted directly to the pivotally mounted armature 24. The blocks 33 dampen 305 the vibrations of armature 24 to such an extent that the irregular vibrations and noises, such as are caused by engagement of the needle with the tablet 41, are suppressed. Therefore, the dampening action of said blocks, aided by the action of dampening member 32, cause the vibrations that result in pure or musical sounds, to be effective in vibrating the armature 24 to induce electrical effects or currents of variable E. M. F. in the coil 22. These induced currents are ampli- 115 fied'by the thermionic valves 36 and are converted into mechanical effects or sound waves by the loud speaker 37.

While the embodiment of the invention illustrated on the drawings has been described with 320 considerable particularity it is to be expressly understood that the invention is not limited thereto, as the invention is capable of being embodied or carried out in a variety of ways, some of which will now readily suggest themselves to those skilled in the art, while changes may be made in the details of construction and arrangement without departing from the spirit of the invention. For convenience of definition the sounds which were originally recorded on the record tablet and which it is desired to reproduce, will be referred to as pure sounds or vibrations, whereas foreign sounds and noises resulting from the action and interaction of the mechanical elements, which are vibrated by cooperation with the record tablet, will hereinafter be referred to as irregular sounds or vibrations. While the use of two thermionic valves has been shown in the'amplifying circuit it will be understood that this showing is diagrammatic only,

means for damping the vibration of said transmitting element, and means for damping the vibrations of said armature.

3. In an electromagnetic reproducing and recording device, means for producing a magnetic field, a coil disposed in said field, an armature pivotally mounted adjacent to said coil, a piv otally mounted stylus bar, and a flexible connec-- tion between said armature and said bar.

ALBERTIS HEWITT. 

